Which federal state is Schleswig-Holstein?

EDITORIAL LEARNING AID

Why is this answer correct?

Schleswig-Holstein is the northernmost mainland state and lies between the North Sea and the Baltic Sea on the border with Denmark; on the map it bears the number 1. The numbers 2 to 4 designate other federal states.

Right at the top in the north, between two seas: number 1.

This translation and explanation are editorial learning aids. The official German wording and answer key govern the examination.